Steam generator



- Patented ar. 9, 19' a ,satl

2,313,061 s'r annnaa'roa Martin Frisch, New York, N. Y;, assignor to Foster Wheeler Corporation, New York, N. 32., a corporation of New York Application November 4, 1938, Serial No. 238332 13 Claims. (ct 122-473) This invention relates to steam generators, and

more particularly pertains to a method of, and

apparatus for, the control of superheat in steam generators utilizing two separate furnaces. In accordance with theinvention, gases from the two furnaces pass unmixed through two separate parallel boiler sections, in only one of which is disposed a convection superheater connected in series with a radiant heat superheater located in the furnace serving that boiler section. The degree of superheat at various ratings is controlled by controlling the firing of the two furnaces, and the arrangement is such that a consta t superheat temperature may be maintaine at all ratings.

For example, if a greater proportion of fuel is fired in the furnace serving both sections of the superheater, the superheat temperature will increase, and if less fuel is fired in that furnace, the superheat will decrease. to change the degree of superheat with a very small'change in the relative proportions of the It is thus possible furnacechambers 22 and 2s and in the paths of the gases from the furnaces are banks of inclined steam generating tubes 26 and 21, the lower ends of which enter the drum it while their upper ends are connected respectivelyto the vertical headers 28 and 29, which in turn are each connected by riser tubes 30 and 3! to upper drums 32 and 33. A main steam and water drum 34 is connected fornigculatiqn witir the drum l8 by downoohier tubes 35, and with the drums 32 and 33 by groups-of circulator tubes 36, 3'8, 38 and 39. Arefractory and insulating casing 40 surrounds the downcomer tubes 35, and not only protects these tubesfrom the hot products of combustion flowing from the furnaces, but at the same time provides two separate parallel passes or gas passages through the boiler, each served by a separate fumace. After leaving the boiler, the gases enter the fines or uptakes til amount of fuel fired in the two furnaces, since increasing the superheat or for the purpose of decreasing it.

For a better understanding of'the particular features that characterise the invention, reference may be had to the following description considered in connection with the accompanying drawings forming a part thereof, and in which:

Fig. 1 is a vertical sectional view illustrating more or less diagrammatically one form of steam generator embodying the invention, and

Fig. 2 is a chart showing a group of curves typical of the variations in gas and steam temperatures for various loads, and distribution of firing between the two furnaces;

Referring to the drawings, reference character l0 designates generally a steam generator having a setting II which includes vertical side furnace walls l2 and it, a front furnace wall it, and a rear furnace wall, not shown. A group of closely spaced vertical water tubes I5, l6 and I! which are connected at their upper ends to boiler drum l8 and at their lower ends to headers i9, 20 and 2 I respectively, forms a vertical partition extending between the front and rear walls of the setting, and divides the combustion space into two separate furnace chambers 22 and 23, each of which is independently fired by the burners 24 and 25 respectively. Directly above the and i2.

Boiler feed water from any suitable source is admitted to eoonomizer inlet headers 83 and 6d and flows through the economizer tubes 55 and 66 to outlet headers iii and 68. From these headers the feed water flows through conduits t9 and 50 to an inlet header 5! of economizer section 52, through which the water flows, and enters header 5% from which it flows in parallel paths through the economizer sections 5t and 55 to outlet header 56, whence it is conducted to the boiler circulation by a conduit, not shown. The side and end walls of the furnace chamber 22 are cooled by water wall tubes 51 extending between upper and lower headers 59 and 60 and water wall tubes 58 which extend between upper and lowerheaders El and 62, the headers 59 to 62 being connected with the boiler circulatory system by external connections, not shown. Other water wall tubes 63 in. the front wall of the settingwhich are connected to upper and lower headers 6t and 66,.are also suitably connected with the boiler circulatory system. Similarly disposed water wall tubes protect the rear wall of both furnaces 22 and 23.

Steam from the steam and water drum 34 flows through steam line 66 to inlet header 6! of a: group of radiant heat superheater tubes 68 which line the inner surface of the wall l3 of the furnace chamber 23, and which are connected at their lower ends to return header 69. From this header certain of the superheater tubes conduct the steam to an upper header l0, whence the steam passes through steam line H and inlet header 12 to another group of radiant heat superheater tubes 73, lining the inner surface of the front wall of furnace chamber 23, and which are connected at their lower ends to a return header 14. From the header ll steam is returned through the tubes 73 which connect the return header i4 and the outlet header 16, whence steam is conducted through line 11 to inlet header 18 of a convection superheater section 19. Steam flows through this superheater section to a final outlet header 80, and thence to the point of use. 7

As diagrammatically shown in the drawings, fuel in the form of pulverized coal is fed to the burners 24 and 25 through fuel lines BI and 82 from a mill 83. Variable amounts of fuel may be supplied to each burner, and the relative rates of firing of the two furnaces thereby controlled by means of a fuel proportioning valve 84 directly connected to the dis charge of mill exhauster 85. Or if desired, two separately controlling exhausters may be used with one mill, or separate mills for each furnace may be employed.

It will be perceived, since all of the superheating surface, both radiant and convection, is positioned either within the furnace chamber 23, or within the section of the boiler served by that furnace, that the final steam temperaturemay be directly controlled by varying the intensity of the firing of burner 25.

The curves in Fig. 2 of the drawings show graphically the calculated operating data for the steam generator embodying the invention. The dotted line curves show the efiect on the performance at all loads of equally firingboth furnaces. Under these conditions, the natural characteristics of radiant and convection superheaters determine the final steam temperature. The discrepancy between the dotted line C, hereafter described, and the desired solid line C, is eliminated by unequally firing the two furnaces. The solid line curves show the effect on the performance when firing to produce the desired final steam temperature curve shown by solid line C. The lowermost curves designated A, show the respective calculated firing rates of the two furnaces at all boiler capacities from-30% to 120% to attain this result. The curves designated B show the temperature of the steam leaving the radiant section of the superheater at all loads within the load range previously mentioned. The curves designated C illustrate the temperature of the steam leaving the convection section of the superheater'or the final temperature of the steam leaving the stem generator at all ratings within the range mentioned. Curves D show the temperature of the gases leaving the convection section of the superheater. Curves E show the temperature of the gases entering the convection superheater. Curves F show the temperature of the gases leaving the furnaces.

In Fig. 2, furnace 22 is designated the water wall furnace, and furnace 23 is designated the superheater furnace. With these furnaces fired respectively as indicated in the full line curves A, constant superheat temperature will be maintained at all ratings from 30% to 120%, as shown in the full line curve C of final steam temperature. It will be observed from an inspection of full line curves A that more fuel will be fired in the superheater furnace whenever the dotted curve C falls below the desired solid curve C and more in the water wall furnace when the reserve is true. The usual deficiency in superheat at low loads in ordinary steam generating and superheating arrangements 'is eliminated by utilizing the present invention by firing more fuel in the superheater furnace and lessin the water wall furnace. This relative firing in the two furnaces produces the double effect of increasing heat input into the steam in the radiant superheater section as shown by full line curves B, and transmitting more arid hotter gases to the convection superheater section as shown by full line curves D, resulting in an increase in the total superheat at the outlet of the convection superheater section. As the load goes up, the difference in the firing rate betweenthe two furnaces decreases as clearlyshown in full line curves A, up to about load when both furnaces are fired equally. From above 75% to about 103%, due to the natural characteristic, the degree of superheat increases if the firing is equalin both furnaces, as indicated in the dotted line of curve C, in consequence of which the firing is reduced very slightly in the superheater furnace and increased in the water wall furnace, so as to maintain the superheat temperature at the desired temperature which will be on the full line curve C. Above 103%, the firing rate in the superheater furnace is slightly increased and in the water wall furnace correspondingly decreased to maintain the desired steam temperature. Since both the radiant and convection superheater sections in the design selected for illustration are subjected to the heat of approximately one-half of the total fuel fired in both furnaces,

the drooping partof the superheat characteristic appears sooner than in ordinary designs and begins in this instance at about of load, and

consequently, except for the small instance between 75% and 103% of load, the superheater furnace always has slightly more fuel fired therein than the water wall furnace so that the final steam temperature will be maintained at the required value. Obviously, both the radiant and convection superheater sections may be proportioned to best suit desired operating conditions so that the inequalities between the firing rates of the two furnaces at varying loads may be different from those shown.

With steam generating and superheating arrangements embodying the invention, the final steam temperature, may be maintained constant by controlling the firing of the superheater and water wall furnaces in the manner indicated in Fig. 2. The rate of firing of the two furnaces will be different excepting at one particular point, which will depend upon the characteristics of the design and the operating conditions. In

this instance, this point is at about 75% of load. With equal firing of the furnaces throughout the entire load range, it will be observed that the final steam temperature varies within but a narrow range. As shown in the dotted line curve C, it will vary from about 880 F. at 30% load to 910 at 90% load, after which it drops to about 900 at load, so that very little control and hence ,very small inequalities in the firing rate of the two furnaces are needed to produce the desired constant steam temperature curve.

Quite obviously, the particular arrangement and disposition of the steam generating and superheating section of the design selected for illustration may be varied without departing from the principles of the invention. For example, the two sections of the steam generator may be in clifierent settings with both sections connected into the same circulatory system. Additionally, the radiant superheater section may be disposed in one or more of the walls of the radiant superheater furnace and if desired, it may be disposed in all of the walls thereof. Moreover, the saturated steam may be conducted from the steam and water drum first to the convection superheater section and thereafter to the radiant section. Means other than that disclosed may be utilized for controlling the rate of firing of the burners in the two furnaces. Such means may include automatic means responsive to the steam temperature to provide unequal firing in the desired direction and automatic meansresponsive to the pressure so as to maintain the firing rate at the desired value to produce the desired steam flow. For example, the final steam temperature or the steam temperature leaving the radiant superheater, or both, may be arranged to govern the temperature control whether the steam flow is to the radiant superheater first or is reversed.

. steam which comprises firing fuel burners to pro- More than one burner may, of course, be utilized in each furnace. I

Since the invention is not limited to the form selected for illustration, it will be understood that the only limitation thereon is the scope of the appended claims.

What is claimed is:

l. The method of generating and superheating steam which comprises producing a separate stream of gases in each of a plurality of furnaces within a setting, fiowing each of said streams of gases unmixed with gases of another stream in heat exchange relationship with steam generat-ing surface, controlling the streams of gases to regulate the heat content thereof, and superheatingthe steam so generated by passing it through separate zones in heat exchangerelationship with one of said streams of gases, one zone being outside the main portion of the path of said one stream of gases and another zone being substantially within the path of said one stream of gases, thereby substantially maintaining the superheated steam at a predetermined temperature at different rates of steam generation without substantially varying the relative heat content of said streams of gases.

2. The method of generating and superheating steam which comprises firing fuel burners to produce separate streams of gases, flowing each of said streams of gases unmixed with gases of another stream in heat exchange relationship with steam generating surface, controlling the firing of the fuel burners to regulate the heat content of the streams of gases, and superheating the a fuel burners.

3. The method of generating and superheating steam which comprises producing separate streams of gases, flowing each of said streams of gases unmixed with gases of another stream in heat exchange relationship with steam generating surface, controlling the streams of gases to regulate the heat content thereof, and superheating the steam so generated by passing it through separate zones in heat exchange relationship with one of said streams of gases, one zone being outside the main portion of the path of said one stream of gases and another zone being substantially within the path of said one stream of gases,

thereby substantially maintaining the superheatedsteam at a constant temperature at different rates of steam generation without substantially varying the relative heat content of said streams of gases. I 1

4. The method of generating and superheating duce separate streams of gases, flowing each of said streams of gases unmixed with gases of another stream in heat exchange relationship with steam generating surface, controlling the firing of the fuel burners to regulate the heat content of the streams of gases, and superheating the steam so generated by passing it through separate zones in heat exchange relationship with one of said streams of gases, one zone being outside the main portion of the path of said one stream of gases and another zone being substantially within the path of said one stream of gases, thereby substantially maintaining the superheated steam at a constant temperature at difierent rates of steam generation without substantially varying the relative firing rate of the fuel burners.

Y 5. Apparatus for generating and. superheating steam comprising a setting, separate steam generating sections in the setting, a furnace for each section, means for firing each furnace to produce a stream of gases therein, means for regulating the firing of each furnace; said sections being so constructed and arranged that the stream of gases produced in the furnace of one of the steam generating sections flows through that section unmixed with gases'produced in the other section, means for superheating the steam generated in said apparatus comprising a radiant superheater section associated with one of said furnaces and disposedj'outside the main portion of the path of the gases flowing therethrough, and a convection superheater section connected to said radiant section and disposed substantially in the path of the gases produced in said one furnace, whereby the superheated steam is maintained substantially at a predetermined temperature at different rates of steam generation with-- out substantially varying the relative firing rate of said furnaces.

6. Apparatus for generating and superheating steam comprising a setting, separate steam generating sections in the. setting, a furnace for each section, means for firing each furnace to produce a stream of gases therein, means for regulating the firing of each furnace, said sections being so constructed and arranged that the stream of gases produced in the furnace of one of the steam generating sections flows through that section un-- mixed with gases produced in the other section,

means for superheating the steam generated in said apparatus comprising a radiant superheater section associated with one of said furnaces and disposed outside themain portion of the path of the gases flowing therethrough, and a convection superheater section connected to said radiant section and disposed substantially in the path of the gases produced in' said one furnace, whereby the superheated steam is maintained substantially at a constant temperature at different rates of steam generation without substantially varying the relative firing rate of said furnaces.

7. Apparatus according to claim 5 in which the means for'firing eachfurnace comprises a fuel burner.

8. Apparatus according to claim 6 in which the means for firing each furnace comprises a fuel burner.

ing steam which comprises producing separate streams of gases, flowing each of said streams of gases unmixed with gases of another stream in heat exchange relationship with steam genpath of said one stream of gases, and controlling the streams of gases to regulate the heat content thereof to thereby control the rate of steam generation and to maintain the superheated steam substantially at a predetermined temperature at different ,rates of steamgeneration.

ll. Apparatus for generating and superheating steam comprising a setting, separate steam generating sections in the setting, a furnace for each section, means for firing each furnace to produce a stream of gases therein, said sections being so constructed and arranged that the stream of gases produced in the furnace of one of the steam generating sections fiows through that section unmixed with gases produced in the other section, means for superheating the steam generated in said apparatus comprising a superheater section associated with one of said furnaces and disposed outsidethe main portion of 'the path of the gases flowing therethrough, said superheater being subject to the radiant heat from said gases and a convection superheater section connected to said first-mentioned supering steam comprising a setting, separate steam 9. Apparatiis according to claim 5 in which the furnaces are provided with water walls. 10. The method of generating and superheatgeneratlng sections in the setting, a furnace for each section, means for firing each furnace to produce a stream of gases therein, said sections being so constructed and arranged that the stream of gases produced in the furnace of one of the steam generating sections flows through that section unmixed with gases produced in the other section, means for superheating the steam generated in said apparatus comprising a superheater section associated with one of said furnaces and disposed outside the main portion of the path of the gases flowing therethrough, said superheater being subject to the radiant heat from said gases and a convection superheater section connected to said first-mentioned superheater section and disposed substantially in the path of the gases produced in said one furnace, and means for regulating the firing of each fur nace to control the rate of steam generation and to maintain the superheated steam substantially at a constant temperature at different rates of steam generation.

13. Apparatus for generating and superheating steam comprising a setting, separate steam generating sections in the setting, a furnace for each section, means for firing each furnace to produce a stream of gases thereip said' sections being .soconstructed-and eurar'rg'ed that the stream of gases produced in the furnace of one of the steam generating sections flows through that section unmixed with gases produced in the other section, means for superheating the steam generated in said apparatus comprising a superheater section having tubes along a Wall enclosing one of said furnaces and a convection superheater section connected to said first-mentioned superheater section and disposed substantially in the path of the gases produced in said one furnace, and means for regulating the firing of each furnace to control the rate of steam generation and to maintain the superheated steam substantially at a predetermined temperature at difierent rates of steam generation.

MARTIN FRISCH. 

